When rotary drilling for petroleum producing wells, it is well known that drilling fluids provide multipurpose uses, such as to remove drill cuttings from the bottom of the hole to prevent interference with the cutting action of the drill bit, to cool and lubricate the drill bit and drill stem and to transport the cuttings to the surface. The drilling fluid also provides support for the walls of the well bore to prevent sloughing of soft formations and provides sufficient hydrostatic head pressure to prevent entry of formation fluids into the well bore. Further, the drilling fluid provides a filter cake lining for the well bore to prevent loss of drilling fluid into certain types of earth formations.
As explained in the above-identified related application, conventional apparatus used for circulating the drilling fluid, typically referred to in the industry as drilling mud, into the well bore typically includes a pump to force the drilling fluids through a hose and swivel into a kelly, which is a non-circular tube that is rotatated by means of a rotary drive mechanism having a non-circular opening through which the kelly is lowered while being continuously rotated. The drilling fluid then flows downwardly through sections of drill stem connected to the kelly and, after exiting the drill bit at the lower extremity of the drill stem, flows upwardly through the annulus between the drill stem and well bore. The drilling fluid then exits the well bore through a fluid return line connected to the well head and is discharged into a settling tank or pit or a series of tanks from which the pump returns the drilling fluids to the well. To monitor this circulation, the related application describes an improved system to measure the level of drilling fluid stored in the tank, as well as the flow of drilling fluid into and out of the well. The monitoring system described in the related application is incorporated in this application by reference to simplify a complete understanding of this invention.
Although the flow of drilling fluid returning from the well bore through the wellhead and passing through the return line can be measured as explained in the related application, it has been found that it is extremely difficult to determine the flow rate of fluid flowing through a pipe with a circular internal cross-section under circumstances where the pipe is less than completely filled with fluid. This difficulty exists because, as the fluid level changes within the pipe, the arc across the pipe varies and thus the cross-sectional area defined by the fluid within the pipe also varies. Because of the partially circular cross-sectional configuration defined by the fluid within the return line, it is extremely difficult to determine the flow rate of fluid returning from the well bore. Accordingly, it is desirable to provide apparatus that simplifies the measurement of the volume of drilling fluid flowing through the return line.
One of the more important functions provided by the drilling fluid is the maintenance of sufficient hydrostatic head within the well bore to maintain a bottom hole pressure that will exceed the formation pressure of any formation intersected by the well bore. If the hydrostatic head pressure is insufficient due to losses of fluid into the formation, the possibility of a well blowout increases substantially.
Accordingly, it is a primary object of the present invention to facilitate a simplified determination of the volume of drilling fluid flowing through a drilling fluid return line by including a portion in such line which has an internal cross-section of parallelogram shape and measuring the flow of drilling fluid returning to the surface by measuring the level of fluid flowing through the parallelogram cross-section.
It is also a feature of the present invention to provide novel means for monitoring the drilling fluid system of well drilling apparatus such that a comparison is provided that indicates drilling fluid being pumped into a well bore and drilling fluid flowing from the well bore.
It is another feature of this invention to provide a novel drilling fluid monitoring system wherein electrical signals representing the level of drilling fluid within the holding tanks, the volume of drilling fluid pumped into the well and the volume of drilling fluid flowing from the well are correlated electronically and displayed for visual inspection.
An even further feature of this invention concerns the provision of a drilling fluid monitoring system wherein an electrical signal reflecting the volume of flow of drilling fluid exiting the well bore is displayed graphically to provide a rapid means for detecting loss of drilling fluid to the formation being drilled.
Other and further objects, advantages and features of this invention will become apparent to one skilled in the art upon consideration of the teachings hereof. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the invention.